BACKGROUND OF THE INVENTION Many tools have been designed to inhibit flat headed screwdrivers from slipping off a screw. For example, GB-A-2 251 196 discloses a screwdriver provided with a coil spring around the shank of the screwdriver which biases a tubular body toward the head of the screwdriver. Initially, the tubular body extends beyond the head and is inhibited from slipping off the head by the wide flat dimensions of the head. In use, the part of the tubular body beyond the head can accommodate the head of a screw so that the screw is substantially aligned with the axis of the screwdriver and inhibits the head of the screwdriver from slipping off. When the tubular body abuts the item into which the screw is being urged, the coil spring allows the tubular body to move relative to the shank so the screw can be screwed all the way into the item.

Other, more complex tools are disclosed in US-A-3 633 640 and US-A-4 800 788, for example.

However, the problem with such tools is that they are relatively complex in construction and dimension, lack the necessary sturdiness or a combination of all three. Many known tools are simply too intricate in construction to withstand the rigours of a toolbox for any economically useful period. Those tools which have better longevity and those of simpler, but poor construction are known to suffer from another problem, that is,"play". Typically, this play manifests itself in the body of the tool through rotational movement across the longitudinal axis of the screwdriver.

Such play is unwelcome because the tool can no longer perform its intended function to a satisfactory standard. For example, play can allow the axis of the screwdriver to be misaligned with the axis of the screw to such an extent that, upon application of pressure to the screw, the screwdriver slips off the screw. Thus, the lifespan of the tool is curtailed, primarily as a result of the aforementioned factors.

Another problem with prior art devices is the perception of the product at point of sale. Many potential purchasers tend to"stress"the device to assess its quality of construction. Because of the poor and relatively complex construction of many prior art devices, a potential purchaser of the item is discouraged from purchasing the item, primarily due to a"loose"and poor quality feel.

It is an aim of the present invention to inhibit some or all of the aforementioned difficulties.

SUMMARY OF THE PRESENT INVENTION According to the present invention there is provided a screwdriver comprising a shank having a working end, abutment means on said shank, an elongate member which is slidably mounted on said shank and comprises a screw receiving portion, a spring retaining portion and a stop which separates said screw receiving portion and said spring retaining portion, spring means on said shank within said spring retaining portion between said stop and said abutment means for biasing said elongate member toward said working end, and a cap fast with one end of said elongate member, the arrangement being such that said stop and at least one of said cap and said abutment means inhibit play of said elongate member across the longitudinal axis of said shank and contact between said cap and said abutment means limits travel of said elongate member in the direction of said working end.

Advantageously, said stop and said cap are substantially in contact with said shank.

One advantage of this is that the shank can move relatively freely, whilst at the same time inhibiting play of the elongate member. Another advantage is that the construction is more resilient and less likely to fail.

Preferably, the separation between said shank and said first stop and said second stop is between 0. 1 5mm and 0.35mm.

Advantageously, said separation is 0.25mm.

Preferably, said stop comprises a shoulder which extends internally of said elongate member.

Advantageously, said shoulder extends around the entire internal circumference of said elongate member.

Preferably, said stop is constructed integrally with said elongate member.

Advantageously, said cap comprises an annular ring.

Preferably, in use, the position of said abutment means on said shank can be adjusted.

Advantageously, said abutment means comprises a collar.

Preferably, said spring means comprises a coil spring mounted around said shank between said stop and said abutment means within said spring-retaining portion, the arrangement being such that, in use, said coil spring urges said elongate member to a first position at a head of said screwdriver.

Advantageously, in use, in said first position said screw-retaining portion extends beyond said head.

Preferably, in use, said elongate member can be urged to a second position, in which said head protrudes from said elongate member.

Advantageously, movement of said elongate member beyond said first position is inhibited by said cap.

Preferably, movement of said elongate member beyond said second position is inhibited by said coil spring.

Advantageously, said spring retaining portion and said screw retaining portion occupy approximately two thirds and one third of the length of said elongate member respectively.

Preferably, the diameter of said spring retaining portion is greater than the diameter of said screw retaining portion.

Advantageously, in use, said elongate member can remain stationary whilst said shank rotates.

Preferably, said screwdriver further comprises a handle mounted on said shank.

Advantageously, said screwdriver is a manual screwdriver.

Preferably, the internal diameter of said screw retaining portion is between approximately 6mm and 8mm.

Advantageously, said internal diameter is 7mm.

Preferably, the internal diameter of said stop is between approximately 4. sum and 6.5mm.

Advantageously, said internal diameter is 5. 5mm.

Preferably, the length, in equilibrium, of said spring retaining portion is between approximately 16. 5mm and 18. 5mm Advantageously, said length is 17. 5mm.

Preferably, in equilibrium, the distance between the head of said screwdriver and the end of said screw retaining portion is between approximately, 1. 5mm and 3.5mm.

Advantageously, said distance is 2.5mm.

It will be appreciated that the above dimensions are subject to the usual manufacturing tolerances involved with casting, machining etc.

Preferably, the head of said screwdriver comprises two generally curved surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention reference will now be made, by way of example only, to the accompanying drawings in which Figs. 1 and 2 show in schematic cross section part of a first embodiment of a screwdriver in accordance with the present invention; Fig. 3 shows in schematic cross section part of a second embodiment of a screwdriver in accordance with the present invention; Fig. 4 shows in schematic cross section part of a third embodiment of a screwdriver in accordance with the present invention; Fig. 5 shows a schematic transverse cross section though the shank of the screwdriver shown in Fig. 4; Fig. 6 shows in schematic cross section part of a fourth embodiment of a screwdriver in accordance with the present invention; and Fig. 7 shows in schematic cross section part of a fifth embodiment of a screwdriver in accordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring to Figs. 1 and 2 a screwdriver in accordance with the present invention is generally identified by reference numeral 10. Screwdriver 10 comprises a shank 12 upon which is mounted a moulded plastic handle (not shown) as is well known in the art. The shank 12 further comprises a collar 14 which is affixed thereto.

An elongate tube 16 is mounted on the shank 12 so that their longitudinal axes are co-axial. The elongate tube 16 comprises a shoulder 18, a screw retaining portion 20 and a spring retaining portion 22. The elongate tube 16 and shoulder 18 are generally

annular in axial cross section and the length of the screw retaining portion 20 and the spring retaining portion 22 are approximately one third and two thirds of the length of the elongate tube 16 respectively. The screw retaining portion 20 of the elongate tube 16 is smaller in internal diameter than the internal diameter of the spring retaining portion 22.

A cap 24 encloses one end of the elongate member 16 and is affixed thereto by means of glue. A coil spring 26 extends around the shank 12 and is housed under compression in the spring retaining portion 22 of the elongate tube 16, between the shoulder 18 and the collar 14. By virtue of the shoulder 18, the collar 14 and the compression of the coil spring 26 the elongate tube 16 is biased toward the head, or working end, of the screwdriver 10 until the cap 24 abuts the collar 14 and inhibits any further movement.

It will be noted that the head of the screwdriver 10 comprises a generally curved portion 28 at either side thereof. The head of the screwdriver 10 is thus smaller in longitudinal dimension than traditional flat head screwdrivers which have two long flat bevelled surfaces at their head. This allows the elongate tube 16 to be shorter because the shoulder 18 can be nearer the head, whilst at the same maintaining the advantages of the present invention. Thus construction costs and time are reduced.

The dimensions of the screwdriver 10, as shown in Fig. 1, are: Dl = Smm D2 = Dl + 2mm = 7mm D = Dl + 0. 5 = S. Smm d2 = 0. 14dl = 0. 77mm Li = 7.51/dl = 17. 60mm (in equilibrium position) II = 0. SDI = 2.5min It will be appreciated that the above dimensions are subject to the usual manufacturing tolerances involved with casting, machining etc. of such a screwdriver.

In use, the screw retaining portion 20 is brought up to the head of a screw (not shown) and placed therearound. Simply by twisting the screwdriver 10 the slot of the screw head can be found without difficulty. Pressure and rotation are applied to the screwdriver 10 in order to screw the screw into an item (not shown). If desired, the

elongate tube 16 can be gripped and held stationary whilst the screwdriver 10 is turning. When the leading edge of the elongate tube 16 contacts the item the coil spring 26 is compressed as the collar 14 moves toward the shoulder, and the elongate tube 16 moves relative to the shank 12. Once the screw has been securely screwed into the item the screwdriver 10 is removed and the elongate member"springs" forward under the compression of the coil spring 26 until the cap 24 abuts the collar 14.

The annular space between the shank 12 and the shoulder 18 and the opening 27 in the cap 24, is 0.25mm respectively. Similarly, the clearance between the outside of the collar 14 and the inside of the spring retaining portion 22 of the elongate tube 16 is about 0.25mm. This arrangement is important because it allows the shank 12 to move smoothly through the elongate tube 16 whilst at the same time inhibiting play of the elongate tube 16 across the longitudinal axis of the screwdriver 10.

The clearance between the maximum width of the head of the screwdriver 10 and the screw retaining portion 20 is lmm at either side. It has been found that this size of clearance is particularly advantageous because it allows a greater range of screws to be accommodated whilst at the same time maintaining the function of the screw retaining portion 20.

Various modifications to the arrangement described are envisaged. For example, the diameter of the opening 27 in the cap 24 could be larger so that the interaction of the collar 14 and the elongate tube 16, together with the interaction of the shoulder 18 with the shank 12 is responsible for reducing play between the elongate tube 16 and the shank 12. Alternatively, the diameter of the opening 27 in the cap 24 could be smaller so that the interaction of the cap 24 and the shank 12, together with the interaction of the shoulder 18 with the shank 12 is responsible for reducing play between the elongate tube 16 and the shank 12.

As shown in Figs 3,4 and 6 the cap 24 may be a screw fit with the elongate tube 16. Such an arrangement would permit the elongate tube 16 and coil spring 26 to be removed from the shank 12 for cleaning purposes or to allow the screwdriver 10 to function as a traditional screwdriver.

The collar 14, which is preferably glued, welded or crimped on the shank 12, could be constructed integrally with the shank 12 of the screwdriver 10, although this would make the construction of the screwdriver 10 more complicated. Alternatively lugs 30 may be swaged on the shank 12 as shown in Figs. 4 and 5. Alternatively and as shown in Fig. 6, the collar 14 could comprise a split ring or circlip which is placed

around a suitably dimensioned groove in the shank 12 so that it protrudes above the shank 12. As another alternative, shown in Fig. 7, the shoulder 18 comprises a split ring or circlip located in a suitably dimensioned groove in the elongate tube 16. The collar 14 could also be adjustable so that the dimension 11 of the screw retaining portion 20 can be adjusted to accommodate screw heads of different sizes.

The coil spring 26 could be replaced by any suitable resilient biasing means (or spring means).

It will be appreciated that the invention is equally applicable to screwdrivers for hand held power tools.